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  • 1
    Electronic Resource
    Electronic Resource
    Facilitation of somatosensory evoked potentials by exploratory finger movements (1993)
    Springer
    Experimental brain research 95 (1993), S. 330-338 
    Details
    ISSN: 1432-1106
    Keywords: Somatosensory processing ; Somatosensory ; evoked potentials ; Microneurography ; Movement ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Modification of somatosensory processing depending on the behavioral setting was studied. Active alternating movements of the fingers, passive tactile stimuli to the hand, and active exploration of objects were performed during recording of somatosensory evoked potentials (SEPs). SEPs were elicited by compound electrical median nerve stimulation and electrical stimulation at detection threshold of cutaneous median nerve fascicles identified by microneurography. Electrical stimulation was not time-locked to the studied condition. In comparison with SEPs at rest there was attenuation of early cortical potentials up to 25 ms post-trigger in all nonresting conditions. In stimulation of the compound median nerve as well as of isolated cutaneous fascicles of a hand actively exploring an object there was an additional increased negativity, peaking at 28 ms. This facilitory effect was independent of attentional focusing and was absent during exploration using the ipsilateral, non-electrically stimulated hand. In patients with parietal lesions the facilitatory effect was diminished on the affected side. Spline interpolated brain maps at this latency based on 32channel recordings in healthy volunteers showed a shift of local contralateral positive maximum from frontal to parietal during exploration, indicating enhancement of a tangential dipole. It is suggested that in conditions involving close sensorimotor interaction such as exploratory hand movements there is preactivation of a cortical area which is located in the central sulcus and receives cutaneous somatosensory inputs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229790
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Comparing Regularized and Non-Regularized Nonlinear Dipole Fit Methods: A Study in a Simulated Sulcus Structure (1999)
    Springer
    Brain topography 12 (1999), S. 3-18 
    Details
    ISSN: 1573-6792
    Keywords: EEG/MEG ; Nonlinear dipole fit ; Simulated annealing ; Regularization ; Truncated singular value decomposition ; Finite element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The inverse problem arising from EEG and MEG is largely underdetermined. One strategy to alleviate this problem is the restriction to a limited number of point-like sources, the focal source model. Although the singular value decomposition of the spatio-temporal data gives an estimate of the minimal number of dipoles contributing to the measurement, the exact number is unknown in advance and noise complicates the reconstruction. Classical non-regularized nonlinear dipole fit algorithms do not give an estimate for the correct number because they are not stable with regard to an overestimation of this parameter. Too many sources may only describe noise but can still attain a large magnitude during the inverse procedure and may be indiscernible from the true sources. This paper describes a nonlinear dipole fit reconstruction algorithm with a new regularization approach for the embedded linear problem, automatically controlled by the noise in the data and the condition of the occuring least square problems. The algorithm is stable with regard to source components which “nearly” lie in the kernel of the projection or lead field operator and it thus gives an estimate of the unknown number parameter. EEG simulation studies in a simulated sulcus structure are carried out for an instantaneous dipole model and spatial resolution in the sulcus and stability of the new method are compared with a classical reconstruction algorithm without regularization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022281005608
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Chiroptical detection. Novel possibilities of its application to enantiomers (1988)
    Springer
    Chromatographia 25 (1988), S. 182-188 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Detection, chiroptical, polarimetric, circular dichroic ; Enantiomers ; Sorbents, optically active
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Polarimetric and/or circular dichroic detection of enantiomers after liquid chromatography on optically active sorberts has been used for the following purposes: determination of enantiomeric purity in spite of peak overlap, investigation of enantiomerization during chromatography, monitoring of racemizations and recording of circular dichrograms without preparative enrichment of enantiomers. Novel examples for all applications are give. The general prospects for chiroptical detection are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02316442
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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